Role of the bilayer in the shape of the isolated erythrocyte membrane.
ABSTRACT The determinants of cell shape were explored in a study of the crenation (spiculation) of the isolated erythrocyte membrane. Standard ghosts prepared in 5 mM NaPi (pH 8) were plump, dimpled disks even when prepared from echinocytic (spiculated) red cells. These ghosts became crenated in the presence of isotonic saline, millimolar levels of divalent cations, 1 mM 2,4-dinitrophenol or 0.1 mM lysolecithin. Crenation was suppressed in ghosts generated under conditions of minimal osmotic stress, in ghosts from red cells partially depleted of cholesterol, and, paradoxically, in ghosts from red cells crenated by lysolecithin. The susceptibility of ghosts to crenation was lost with time; this process was potentiated by elevated temperature, low ionic strength, and traces of detergents or chlorpromazine. In that ghost shape was influenced by a variety of amphipaths, our results favor the premise that the bilayer and not the subjacent protein reticulum drives ghost crenation. The data also suggest that vigorous osmotic hemolysis induces a redistribution of lipids between the two leaflets of the bilayer which affects membrane contour through a bilayer couple mechanism. Subsequent relaxation of that metastable distribution could account for the observed loss of crenatability.
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ABSTRACT: Membrane injury of hemolyzing erythrocytes was observed under scanning electron microscopy by a method which enabled fixing of the holes at the moment of their formation. When the cells were lysed at room temperature, the injury consisted of a long, narrow tear dividing the cell in two halves. The rupture was identical in appearance when the cells were caused to lyse at 49.5 C, in which case the cytoskeleton was denatured and the membrane consisted mainly of the lipid bilayer. If an amphipathic detergent, lysophosphatidylcholine (LPC), was present in the lysing medium, circular holes were formed in the membrane. The results show that lipids control the appearance of the hemolytic hole. The formation of the long tear can be attributed to a wavy instability that arises in the membrane after the connections between the membrane layers are damaged. These layers begin to oscillate so that the distance between them changes periodically. When the oscillation is of a squeezing wave mode, a local thinning develops, leading to a tear in the membrane. The round holes formed in the presence of LPC can be explained by globular micelles formed by the LPC along the edges of the growing hole at the moment of its formation.Journal of Biological Physics 02/1987; 15(1):22-25. · 0.95 Impact Factor
Article: Shape control in the human red cell.[Show abstract] [Hide abstract]
ABSTRACT: When the human red cell consumes its ATP, the cell loses its discoid character in favour of a spiculated and eventually a spherical form. This discocyte-echinocyte transformation parallels both degradation of phosphatidylinositol 4,5-bisphosphate and phosphatidic acid but not dephosphorylation of cytoskeletal proteins. Dephosphorylation of both spectrin and band 3 lags behind metabolic crenation. Exogenous vanadate accelerates both shape changes and lipid dephosphorylation in a parallel manner during metabolic depletion. In contrast to its effect on lipids, vanadate reduces the rate of protein dephosphorylation. These observations strongly support a shape control mechanism in the red cell, based on phosphoinositide metabolism and compatible with a bilayer-couple model.Journal of Cell Science 03/1986; 80:281-98. · 5.88 Impact Factor
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ABSTRACT: Morphological response (MR) of red blood cells represents a triphasic sequence of spontaneously occurring shape transformation between different shape states upon transfer the cells into isotonic sucrose solution in the order: S(0) (initial discoid shape in physiological saline)-->S(1) (echinocytic shape at the beginning of MR, phase 1)-->S(2) (intermediate discoid shape, phase 2)-->S(3) (final stomatocytic shape, phase 3). In this paper, the dynamics of cell shape changes was investigated by non-invasive light fluctuation method and optical microscopy. Among 12 possible transitions between four main shape states, we experimentally demonstrate here an existence of nine transitions between neighbour or remote states in this sequence. Based on these findings and data from the literature, we may conclude that red blood cells are able to change their shape through direct transitions between four main states except transition S(1)-->S(0), which has not been identified yet. Some shape transitions and their temporal sequence are in accord with predictions of bilayer couple concept, whereas others for example transitions between remote states S(3)-->S(1), S(1)-->S(3) and S(3)-->S(0) are difficult to explain based solely on the difference in relative surface areas of both leaflets of membrane suggesting more complex mechanisms involved. Our data show that MR could represents a phenomenon in which the major role can play pH and chloride-sensitive sensor and switching mechanisms coupled with transmembrane signaling thus involving both cytoskeleton and membrane in coordinated shape response on changes in cell ionic environment.Biochimica et Biophysica Acta 09/2010; 1798(9):1767-78. · 4.66 Impact Factor